Cut all the ingredients and put them in a big saucepan. Cook the sauce until it reaches a thick point and the water in excess has evaporated. Fill the sterilized glass jar and cook at bain-marie for about 15 minutes. If you intend to use the preserve within a month, you can avoid the bain-marie and let the preserve cool completely putting the jars underneath a blanket so to allow them to cool slowly and create the vacuum.